1. Field of the Invention
The invention relates to a support apparatus for a trolley pole and, more specifically, to a design utilizing a spring and a variable length moment arm to minimize the force required to lower the trolley arm to a stowed position.
2. Description of the Related Art
A trolley pole is a device used to conduct electrical current from an overhead fixed conductor such as a trolley line to the electric drive on a rail vehicle. A U-shape electrical conducting shoe located on the end of the trolley pole contacts and captures the trolley line. An electrical cable is attached to the conducting shoe and runs down the trolley pole to the electric drive of the vehicle. A trolley pole support apparatus must maintain a suitable upward force on the trolley pole to keep the conducting shoe in constant physical and, thereby, electrical contact with the trolley line.
Two frequent problems associated with trolley poles are (1) keeping the trolley pole on the trolley line and (2) stowing the trolley pole when not in use.
Standard trolley poles pivot about an arc between an extended position and a stowed position utilizing a coil spring and mechanical linkage to provide pole tension against the trolley line. The mechanical linkage does not provide a constant force to the trolley pole shoe as the pole travels through its arc. As the pole rises the coil spring expands and therefore the force on the trolley pole shoe decreases. In instances where the trolley line is relatively high, as the trolley pole extends upward to reach the trolley line, the spring is extended to such a length that the pole force can reduce almost to the point where there is no longer any force to keep the trolley pole shoe in contact with the trolley line. Consequently, the trolley pole will lose contact with the trolley line and electrical power to the vehicle will be disrupted. On the other hand, in order to move the trolley pole to the stowed position it is necessary to rotate the trolley pole and to compress the spring which requires the application of a high force on the trolley pole when it is needed least.
Typically, the vehicle operator manually positions the trolley pole from the extended position to the stowed position. The closer the trolley pole is brought to the stowed position, the greater the force the operator must exert to keep the pole held down. The operator must therefore exert the greatest force upon the trolley pole to stow it when the pole is not in use. This is opposite the desired situation in which the force to stow the trolley pole is less than the force the trolley pole shoe exerts upon the trolley line in the extended position.
U.S. Pat. No. 488,179 teaches a trolley stand for electric cars utilizing a trolley pole socket piece F having a lateral arm acting against a spring H. The lateral arm provides a long moment arm to urge the shoe against the trolley line when the trolley pole is in the extended position, the spring is extended and provides a short moment arm when the trolley pole is in the stowed position and the spring is compressed. In this manner, the low spring force in the extended position acts upon a larger moment arm to produce a high rotational moment and subsequent high force on the shoe against the trolley line, but the high spring force in the stowed position acts upon a small moment arm to produce a low rotational moment and low force for stowing the trolley pole.
However, as illustrated in FIG. 2 of this patent, the lateral arm F' is limited in its rotation to the stowed position by the wall of cylindrical drum C. Ideally, to minimize the force of the spring against the trolley arm in the stowed position, the lateral arm F' would position the roller F immediately below the pivot F.sup.3. This is impossible with the arrangement of this patent. An apparatus is needed which provides a very low moment arm to the spring force when the trolley pole is stowed.
A trolley pole support apparatus is desired in which the force required to stow the trolley pole is low even, in the stowed position, when the spring associated with the apparatus is in maximum compression.